(From episode 3:)
Ah, yes; a mysterious lock of hair is definitely A Clue. As the great detective himself once put it:
“I gathered up some scattered ash from the ﬂoor. It was dark in colour and ﬂakey - such an ash as is only made by a Trichinopoly. I have made a special study of cigar ashes - in fact, I have written a monograph upon the subject. You can find it there, on the shelf, next to my twelve-volume treatise on the texture and appearance of the hairs found within the crevice between the common British dockworkers’ buttocks. I ﬂatter myself that I can distinguish at a glance the hairs of any known shipping company’s employees, either in a tangle or single strands. It is just in such details that the skilled detective differs from the Gregson and Lestrade type.”
- A Study In Scarlet.